Evaluation And Application Of Water Injection Close To Fracture Pressure For Low Permeability Reservoir In Zhundong Area

For water flooding oil field，enough and high quality water injection is the base ofstabilizing oil field productivity.“The pressure of water injection must not be rated higherthan the reservoir’s fracture pressure” is one of the technical limits for reservoir development.This technical limit for reservoir development can be achieved for mid or highpermeability reservoirs， but for low or extra-low permeability reservoirs， it is difficult toachieve this technical limit. Compared with mid or high permeability reservoirs， thedifficulty for low permeability reservoirs is that water injection is difficult， which causesmany problems，including：The formation energy couldn’t be complemented in time and wellyield declines rapidly， reservoir producing condition is bad， and water displacementefficiency is low. Water flooding development effect is poor.For low permeability reservoirs，there is an obvious starting pressure gradient， and theoil producing capability and the water absorbing ability are very low. The injection wells needhigh injection pressure because of the high starting pressure difference. The geologicalcharacteristics of extra-low permeability reservoirs determine that the water injection mustbase on the high pressure water injection. So subject to the provisions of casing safety， theinjection pressure can be increased to near or slightly higher than the reservoir’s fracturepressure， so that the micro fractures can be formed near the borehole of injection wellswhich can improve the permeability. Under the high pressure， injected water can go into theformation along the micro fractures and displace oil and gas towards to producing wells． bythe connected pores of the rock.